A variety of lightweight, composite beams and stiffeners may be used in vehicles such as aircraft in order to support or strengthen features such as wings and fuselage sections. For example, stiffeners having an “I” cross sectional shape may be used to stiffen wing panels forming part of a wing assembly. These lightweight I-section stiffeners may be typically formed from graphite fiber tape laminates which exhibit relatively high axial stiffness, but relatively low interlaminar toughness, particularly at the intersection of the web and the base/cap.
I-section stiffeners may be fabricated using two preformed C-channels, in which the flanges of the channel are joined to the web by a radius. Due to the radius, the intersection of the base and cap with the web form a void or “radius filler zone” in which a filler may be placed in order to reinforce the stiffener in this area. The stiffener must possess sufficient pull-off strength in the area of the radius filler zone to resist tension loads imposed on the stiffener for a given application. In order to achieve adequate pull-off strength, it may be necessary to increase the gauge of the stiffener, thereby adding weight to the aircraft. Alternatively, radius blocks may be added to the stiffeners in order to increase pull-off strength, but the radius blocks also add undesirable weight to the aircraft.
Accordingly, there is a need for a stiffener construction that exhibits improved pull-off strength in the area around the radius filler zone without materially increasing the weight of the stiffener.